Metallurgical factors affecting the thermal and electrical conductivity of Al and Mg alloys

Controlling the metallurgical factors affecting thermal conductivity is critical for improving thermal conductivity and promoting the wider use of structural materials in automotive, aerospace, and electronics applications. Although numerous studies examine isolated process parameters affecting thermal conductivity, there is a lack of comprehensive review of the effect of process parameters on thermal conductivity. This review critically summarizes the work available in the literature on metallurgical factors influencing thermal conductivity of aluminum and magnesium alloys, evaluating the effects of alloying elements, solidification, heat treatment, porosity, reinforcement addition, and plastic deformation. The review begins by presenting heat transfer mechanisms in metals, focusing on thermal carrier mobility in metals. While pure aluminum and magnesium exhibit relatively high conductivities, lattice irregularities including vacancies, dislocations, grain boundaries, secondary phases, and porosity all contribute to scattering of thermal carriers, thereby reducing conductivity. Studies on alloying have indicated that achieving high conductivity primarily requires minimizing solid solution concentration. Secondary phases in the microstructure also influence conductivity, making manipulation of their volume fraction and morphology refinement advantageous for conductivity. Thereafter, the various methods used to improve conductivity will be discussed, including novel addition of reinforcement particles such as graphene. Thermal conductivity manipulation in light alloys can be achieved via strategic control of composition, altering cooling rates, introducing chemical modifiers, and conducting high-temperature treatments. Finally, the discussion will include inadequacies in the literature as well as the opportunities for future work. To conclude, this review will demonstrate that although similar process techniques can be used to modify both mechanical properties and thermal conductivity, changes in microstructure can produce significantly different and often contrasting effects between these two properties. Therefore, with the comprehensive understanding enabled by this critical review, metallurgical control for enhancing thermal properties can be used in conjunction with that used for mechanical properties, to produce quality aluminum and magnesium components for engineering applications.